Relay control apparatus

Abstract

The operation of an electromechanical relay is synchronized with the power line waveform where an electrical power supply is supplied from a source to an electrical load. The current voltage supplied to the load is characterized by a power line waveform. An electromechanical relay is positioned between the power supply and the load where contacts of the relay are opened and closed to interrupt and supply power to the load. A microcontroller is positioned between a power source and the electromechanical relay and actuates the relay so that when the contacts are closed or opened the contacts are not exposed to an undesired voltage. A feedback control circuit senses the opening and closure of the contacts so that in the event the contacts, for example close at an undesireable point on the load current waveform the microcontroller adjusts for the necessary delay to cause the actuation of the relay to occur such that the contact closure is at the desired point in the load current waveform.

We claim: 
     
       1. Power line synchronization circuitry comprising: an electrical power supply,   an electrical load for receiving current from a power line at a preselected interval in the power line waveform,   a relay positioned between said power supply and said load, said relay including a pair of contacts being movable upon actuation between an open position and a closed position to interrupt and supply power to said load, respectively,   control means for controlling the supply of voltage and current from said power supply to said relay to actuate said relay at a selected interval in the power line waveform so that voltage and current are supplied to and removed from said load just prior to the period of time in the power line waveform when the applied voltage and current is zero,   comparator means for sensing actuation of said relay with respect to the time int he power line waveform when said relay is actuated and transmitting a responsive signal to said control means,   said comparator means transmitting a responsive signal to said control means in the event said contacts open or close,   said control means being responsive to the signal from said comparator means to adjust the supply of voltage and current to said relay to maintain opening and closing of said relay synchronized with a selected interval in the power line waveform and thereby measure the time for actuation of the relay to adjust actuation thereof such that the contacts open and close at the desired point in the power line waveform with respect to the point in the load power line waveform when the voltage and current is zero,   means for superimposing a high frequency signal on top of the power line waveform,   sensing means connected to said relay contacts for receiving said high frequency signal,   said relay upon actuation supplying said sensing means with a signal from the power line,   said sensing means upon actuation of said relay coupling the high frequency signal and the power line signal to generate an output signal to said control means, and   said control means including a microcontroller for measuring the length of time between the actuation of said relay and receipt of the output signal from said sensing means.   
     
     
       2. Power line synchronization circuitry as set forth in claim 1 in which, said means for superimposing a high frequency signal on top of the power line waveform includes as oscillator circuit capacitively coupled to said electrical power supply, and   said oscillator circuit having an operating frequency greater than the frequency associated with said electrical power supply.   
     
     
       3. Power line synchronization circuitry as set forth in claim 1 which includes, filter means for conducting the high frequency signal to said oscillator circuit and preventing conduction of the low frequency signal associated with the power line waveform to said oscillator circuit.